Deciphering the dichotomy exerted by Zn(ii) in the catalytic sp2 C–O bond functionalization of aryl esters at the molecular level

Ni-catalysed functionalization of strong sigma C–O bonds has become an innovative alternative for forging C–C bonds from simple and readily available phenol-derived precursors. However, these methodologies are poorly understood in mechanistic terms. Here we provide mechanistic knowledge about how Ni catalysts enable sp2–sp2 bond formation between aryl esters and arylzinc species by providing reliable access to on-cycle mononuclear oxidative addition species of aryl esters to Ni(0) complexes bearing monodentate phosphines with either κ1- or κ2-O binding modes. While studying the reactivity and decomposition pathways of these complexes, we have unravelled an intriguing dichotomy exerted by Zn(ii) salts that results in parasitic ligand scavenging, oxidation events and NiZn clusters. We provide evidence that coordinating solvents and ligands disrupt these processes, thus offering knowledge for designing more-efficient Ni-catalysed reactions and a useful entry point to unravel the mechanistic intricacies of related processes. Mechanistic details of Ni-catalysed functionalizations of strong sigma C–O bonds in synthetic chemistry have been elusive. Now, the identification and characterization of important Ni species, as well as the role of a ZnCl2 additive and solvent in the coupling of aryl esters, are reported.